Method of inhibiting the formation of fiber-knots in paper pulp and product



United States Patent C) 3,499,823 METHOD OF INHIBITING THE FORMATION OF FIBER-KNOTS IN PAPER PULP AND PRODUCT Ingemar Liss-Albin Croon, Alfredshem, and Lars-Gunnar Samuelsson, Ornskoldsvik, Sweden, assignors to M och Domsjo Aktiebolag, Ornskoldsvik, Sweden, a limited company of Sweden No Drawing. Filed Aug. 22, 1966, Ser. No. 573,817 Claims priority, application Sweden, Aug. 24, 1965, 11,059/ 65 Int. Cl. D21d 3/00 U.S. Cl. 162158 14 Claims ABSTRACT OF THE DISCLOSURE This invention provides a method for inhibiting the formation of difiicultly defibered knots at the cut edges of cut pulp sheet during drying of the pulp sheet, by incorporating in the pulp sheet at the cut edges thereof, eithe before, after, or during cutting, a water-soluble substance capable of maintaining the cellulose fibers spaced apart sufficiently to prevent the formation of cross-links between adjacent cellulose molecules in the respective fibers during drying. There are also provided cut cellulose pulp sheets having incorporated only at the cutting zone of the sheet a water-soluble substance capable of maintaining the cellulose fibers spaced apart sufficiently to prevent the formation of cross-links between adjacent cellulose molecules of the fibers when the pulp is drying.

This invention relates to a method for inhibiting the formation of difficultly defibered fiber-knots (fish-eyes) during the manufacture of cut paper pulp sheet, and to cut paper pulp sheet having only a small amount of and preferably substantially no fiber-knots.

In the manufacture of certain types of pulp and especially short-fiber sulfate pulp and semi-chemical pulp, fiberknots are formed which reduce the usefulness of the pulp for producing paper. The fiber-knots are so difficult to defiber that the majority escape defibration in the beating devices of the paper mill, and pass into the finished paper. They occur as transparent surfaces (shiners) in glazed or calendered papers. Furthermore, the fiber-knots possess absorption properties different from that of the remaining paper, which among other things results in uneven color absorption by the paper during dyeing and printing.

The present invention attacks this problem by inhibiting and preferably preventing the formation of fiber-knots.

In accordance with the invention, a method is provided for inhibiting and preferably preventing the formation of fiber-knots by the combined steps of cutting the pulp sheet and incorporating in the pulp sheet at cut edges thereof, before, after or during cutting, a water-soluble substance capable of maintaining the cellulose fibers spaced apart sufficiently to prevent the formation of crosslinks between molecules of the fibers during drying. Thus, in effect, shrinkage of the cellulose fiber is inhibited or prevented, and fiber-knots are reduced in number, or not formed at all.

The invention is based on the observation that to a large extent fiber-knots are localized at the edges of cut pulp sheets, and that the amount of fiber-knots which can be defibered only with difliculty reaches a maximum at a certain moisture content of the pulp sheets, The amount of fiber-knots is low immediately after cutting, but increases greatly during drying of the pulp, as may occur in storage.

By way of an explanation of what occurs, during the process of the invention, the following is submitted. It is believed that drying results in the removal of water molecules, which are more or less strongly bound to the cellulose molecule in the fiber wall by means of hydrogen bonds. The loss of the Water makes possible direct chemical bonds cross-linking adjacent cellulose molecules together. This can most easily occur at the points of contact between the various fibers, and the better the contact between the undried fibers, the stronger will be the bond. The invention associates this with the number of fiberknots in the pulp, and it inhibits or prevents their formation by preventing such cross-linking.

The invention is applicable to any portion of the cut edge of the pulp sheet or the area or zone adjacent there to. Hence, the term cutting zone is used herein to refer to the portion of the pulp sheet which, on cutting, lies in the near proximity of and is influenced by the cutting tool, or if the pulp sheet has already been cut, the cut edges of the same and the areas adjacent thereto which, during cutting, have been either in contact with or close enough to be influenced by the cutting tool. Normally, the cutting zone extends inwardly from the cut up to approximately 10 mm. from the cut edge.

The inhibition or prevention of the cross-links between adjacent cellulose molecules in the fiber can be effected by a variety of techniques. One way, for example, is by the addition of a substance which causes cellulose to swell, whereby the loss of water does not result in shrinkage. Preferably, such a substance does not itself evaporate during storage of the pulp, The substance in question can itself replace the lost water formerly bound to the carbohydrate molecules in the fiber walls by means of hydrogen bonds.

Another technique is to reduce the loss of water by adding a hygroscopic substance that itself absorbs water from the air. A hygroscopic substance can function by reducing the vapor pressure of the water bound to the cellulose molecule.

A further technique is to add a substance that lowers the surface tension of the capillary bound Water in the pulp, so that the effect of the attracting forces on drying is reduced (reduced Campbell effect), such as by adding a surfactant.

In addition, the formation of fiber-knots in pulp can be reduced, if not eliminated, by introducing into the pulp a substance which by its presence prevents the fibers from coming into such contact with each other that bonding I occurs.

It is to be understood that according to the instant invention any two or more of these techniques can be combined by selecting or combining substances which impart one or more of these effects.

Suitable substances which can be incorporated in the pulp at the cutting zone are the water-soluble polyhydric alcohols having a molecular weight within the range from about 60 to about 1500, and preferably within the range from about 60 to about 200, and a volatility less than Water, i.e. an evaporation number of at least in comparison with diethyl ether, according to the standard method disclosed by H. Gnamm in Die Itisungsmittel and Weichhaltungsmittel (vol. 1, Vierte Aufiage, Stuttgart, 1943, page 319). In this method, a certain quantity of the substance is deposited on a filter paper. Light spots are obtained on the paper, which is then suspended against a light background and the time required before the light spots disappear is determined. A corresponding test is made with the same amount of diethyl ether. The evaporation number for the substance is equal to evaporation time of the substance evaporation time of diethyl ether glycol, tripropylene glycol, dibutylene glycol, and tributylene glycol; and mono and polyalkylene glycols and their ethers and esters, such as ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, and triethylene glycol monoethyl ether, or mixture thereof; and polyoxylalkylene glycols, and their ethers and esters, within the above states molecular weight range. Examples of suitable polyoxylalkylene glycols are poly oxyethylene glycols having a molecular weight within the range from about 200 to about 1500, polyoxypropylene glycols having a molecular Weight of within the range from about 250 to about 1500 and polyoxybutylene glycols having a molecular weight within the range from about 300 to about 1500. These substances cause cellulose to swell, and in certain cases they are also surface active, and hygroscopic.

Suitable hygroscopic substances which can be added to the pulp according to the instant invention thereby reducing the amount of water leaving the pulp on drying are water-soluble salts of the alkali metals and calcium, such as, for example, sodium and potassium chloride, nitrate, sulfate, monoor dihydrogen sulfate, acetate or oxalate and calcium chloride and calcium nitrate. These salts, as a rule possess a high hygroscopicity, and thus act as water retainers, but a number of the same, such as sodium chloride, potassium chloride and sodium sulfate prevent fiber contact and thus prevent bonding of fibers.

These can also be used in admixture. A particularly suitable combination is an aqueous solution containing ethylene glycol and calcium chloride.

Suitable surfactants which can be employed herein in accordance with the instant invention include the polyoxyalkylene glycol ethers which can be defined by the following general formula:

wherein R is a straight or branched chain saturated or unsaturated hydrocarbon group having from about eight to about twenty-four carbon atoms, or an aralkyl group having a straight or branched chain saturated or unsaturated hydrocarbon group of from about eight to about twelve carbon atoms attached to the aryl nucleus, the aralkyl group being attached to A through the aryl nucleus. A is selected from the group consisting of ethereal oxygen and sulfur, amino, carboxylic ester and thio carboxylic ester groups. Y represents a straight or branched chain alkylene group having from two to four carbon atoms and x is a number from about 8 to 20.

R can for example be a straight or branched chain alkyl group, such as octyl, nonyl, decyl, lauryl, myristyl, cetyl or stearyl; an alkylene group, such as hexenyl, dodecenyl, oleyl, linoleyl, ricinoleyl, or linolenyl; or an alkyl aryl group, such as octyl phenyl, nonyl phenyl, decyl phenyl, dodecyl, phenyl, or isooctyl phenyl. Y can be ethylene, l-methylethylene, 1,2-diethylethylene, 1,1- diethylmethylene, 1,3-propylene and 1,4-butylene.

Where R is alkyl, it will be evident that the polyoxyalkylene glycol ether can be regarded as derived from an alcohol, mercaptan, amine, or an oxy or fatty acid of high molecular weight, by condensation with an alkylene oxide, for example, ethylene oxide, 1,2-propylene oxide, 2,3-butylene oxide or 1,2-butylene oxide. Typical of this type of product are the condensation products of oleyl, stearyl, lauryl, palmityl, and myristic alcohol, mercaptan or amine or oleic, lauric, palmitic, myristic or stearic acid, with from 8 to 17 moles of ethylene oxide such as Emulfor-ON, Nonic 218, Sterox SE and Sterox SK. Typical alkyl esters are Renex (polyoxyethylene ester of tall oil acids) and Neutronyx 330, and 331, higher fatty acid of polyethylene glycol.

Where R is aralkyl the polyoxyalkylene glycol ether can be derived from an alkyl phenol or thiophenol.

In addition, polyoxyalkylene alkyl phenols and thiophenols having the following general formula can be employed:

where R is a straight or branched chain saturated or unsaturated hydrocarbon group having from about eight to about eighteen carbon atoms, A is oxygen or sulfur, and x is a number from 8 to 20. R can, for example, be a straight or branched chain octyl, nonyl, decyl, lauryl, cetyl, myristyl or stearyl group. Typical are the condensation products of octyl and nonyl phenol and thiophenol with from 8 to 17 moles of ethylene oxide, available commercially under the tradena-mes Igepal CA and CO, NIW, Antarox A 400, Triton X-100, Neutronyx 600 and Tergitol NFX.

Sulfated polyoxyalkylene glycol ethers of the structure, RA-(YO) Y-OSO M can also be employed. These compounds are in every respect the same as the polyoxyalkylene glycol ethers set out above, with the addition of the sulfate group OSO M, wherein M is a monovalent cation such as hydrogen, an inorganic cation such as sodium, potassium or ammonium or an organic cation such as a highly basic amine, for example, mono-, dior triethanolamine, or tributylamine.

Furthermore, the alkyl aryl sulfonates as a class of anionic Wetting agents are suitable for use herein. One example thereof is sodium dodecyl benzene sulfonate. Another example are the sulfonated phenyl polypropylene alkanes characterized by the branched chain structures of polypropylene and tertiary alkyl carbon at the benzene ring, and having the following general structure:

CHzRz where M is hydrogen, an alkali metal ammonium, or an organic amine cation, R and R are alkyl of the type formula C H and at least one R is a polypropylene group, the whole alkyl group containing preferably 12 to 15 carbon atoms. These are known compounds, whose preparation and properites are set forth in US. Patent No. 2,477,383, to Lewis, issued July 26, 1949; they are available in commerce under the trade names Oronite, Ultrawet, and Neolene.

Other water-soluble alkyl aromatic sulfonic acids which can be used include those prepared by alkylating benzene or naphthalene with a kerosene fraction, followed by sulfonation to aromatic sulfonic acids, such as sodium keryl benzene sulfonate.

Other surfactants suitable for use herein include esters of sulfuric acid with aliphatic alcohols of 10 to 18 carbon atoms, particularly oleic acid, tall oil, turkey red oil, and acids derived by the reduction of the fatty acids derived from coconut oil, palm oil, sperm oil and the like long-chain fatty acids, sulfonated castor oil, esters and ethers of isethionic acid, long-chain fatty acid esters and long-chain alkyl ethers of 2,3-dihydroxypropane sulfonic acid and sulfuric acid esters of monoglycerides and glycerol monoethers.

Also useful are the poly-1,2-alkylene oxide wetting agents described and claimed in US. Patents No. 2,674,- 619 to Lundsted, dated Apr. 6, 1954, and No. 2,677,700 to Jackson et al., dated May 4, 1954. These are condensates of 1,2-alkylene oxides, such as 1,2-propylene oxide or 1,2-butylene oxide, alone or in admixture, and such mixtures can also include ethylene oxide, such as the polyoxypropylene-oxyethylene condensates, the ethylene oxide residues constituting from 20 to of the resulting condensate.

These condensates conform to one of the following two type formulae:

wherein Y is the residue of an organic compound containing therein a single hydrogen atom capable of reacting with a 1,2-alkylene oxide; R R R and R are selected from the group consisting of hydrogen-aliphatic radicals and aromatic radicals, at least one such substituent being a radical other than hydrogen; n is greater than 6.4 as determined by hydroxyl number, and X is a watersolubilizing group.

The substance is added to the pulp sheet in a manner to ensure its incorporation therein by absorption and/or impregnation. Liquids can be added as such in water or in the form of a solution of suitable concentration or in an organic water-miscible solvent such as diacetone alcohol, ethanol, acetone, dimethyl sulfoxide and methanol. If the substances are solid they should be in solution in a suitable solvent, water being preferred.

The amount of substance added to prevent the formation of hydrogen bonds depends on the estimated occurrence of fiber-knots in the material to be treated, and the water retaining effect of the substance in question, and is therefore best determined experimentally in each particular case. Satisfactory concentrations are within the range from about 0.1 to about but this is in no way critical. Preferably, from about 0.5 to about 5%, calculated on the dry weight of the pulp, is used and amounts as large as 25% can be used in some cases.

The active substances according to the invention can be applied to the pulp at the cutting zone of the sheet before, during, or immediately after the cutting, by direct application, dipping, brushing, spraying or coating. It can for instance be applied to the cut edges, after the pulp sheet has been cut. In certain cases, it seems to be particularly advantageous that the substance be present on the cutting edge of the knife or other cutter, during the cutting, or in the cutting zone, so as to obtain optimum penetration into the knife-compressed portions of the pulp.

The following examples in the opinion of the inventors represent preferred embodiments of the invention.

EXAMPLE 1 Pulp sheets of short-fiber sulfate pulp having a moisture content of 20% were cut into squares of 20 by 20 mm., the edges of which were painted, by means of a brush, with polyethylene glycol of molecular weight 600* so that an approximately 2 mm. wide impregnated zone appeared along the edges, in which the concentration of polyethylene glycol was approximately 8%, calculated on the dry weight of the pulp in the zone in question. The material was dried at 60 C. for hours, to accelerate the test, and was then conditioned at C. and a relative humidity of 65% for one day. Six samples each of grams were thereafter defibrated for 20 minutes in an English standard defibrator, whereafter they were supplied to a Bauer-McNet 20 mesh screen, where water was passed through for 20 minutes. Corresponding tests were carried out on untreated material. The residues, made up of fiber-knots remaining on the screen, were weighed. The

results are set out in Table 1 below, which includes an account of the amount of screen residue per unit length of edge for obtaining comparable results.

TABLE I Screen residues, mg.

Polyethylene Untreated glycol treated Sample No sample sample 1 217 138 2 279 3 257 86 4- 317 154 5- 305 187 6 304 216 Average 280 155 Total edge length in meters 12 9 Screen residue, mg./m., edge length. 23 17 The quantity of screen residues constituted a direct measurement of the quantity of fiber-knots in the pulp. It is evident from Table I that the untreated sample contained approximately 35% more fiber-knots than the sample treated according to the invention.

EXAMPLE 2 A short-fiber sulfate pulp sheet having a moisture content of 20% was cut into 10 mm. wide strips. In between the cutting operation the edges of the shears were moistened with polyethylene glycol of molecular weight 400, which was transferred to pulp during cutting. In this way, impregnated zones of approximately 1 mm. in width in the strips were obtained, containing about 5% polyethylene glycol calculated on the dry weight of the pulp.

The samples were dried for 15 hours at 60 C. and thereafter conditioned for one day at 20 C. and a relative humidity of 65%. Thereafter, 5 samples each of 25 grams were defibrated for 15 minutes in an English standard defibrator, and then screened for 20 minutes in a Bauer-McNet 20 mesh screen. Corresponding tests were made on untreated samples. The data obtained on the screen residues are set out in Table II below.

It can be seen from Table II that the untreated sample contained more than double the amount of fiber-knots as the sample treated according to the invention.

EXAMPLES 3 TO 5 A pulp sheet of birch sulfate pulp having a moisture content of 20% was cut into 10 in. wide strips. Between cuttings, the edges of the shears were moistened, in separate tests, with polyethylene glycol of molecular weight 600, diethylene glycol and ethylene glycol, respectively. In this way, about 1 mm. wide impregnated zones were obtained along the edges of the strips, which contained about 5% polyalcohol calculated on the dry weight of the pulp.

The strips were dired at 60 C. for 15 hours after which they were defibrated in water. Circular sheets 20 cm. in diameter and with a surface weight of 100 g./m. were formed from the fiber suspensions obtained. The sheets were glazed in a laboratory calender. Corresponding tests were made with the same pulp without moistening the edges of the shears. The fiber-knots occurring in the glazed sheets appeared as transparent surfaces (shiners). The data obtained is set out in Table III below.

Table III Number of fiber-knots per dm. Untreated 260 Example No.2

(3) Treated with polyethylene glycol 600 230 (4) Treated with diethylene glycol 150 (5) Treated with ethylene glycol 40 The results show that a substantial reduction in the number of fiber-knots was obtained by means of the methods according to the invention, the reduction being more noticeable in the case of low molecular weight polyalcohols.

EXAMPLE 6 A pulp sheet of birch sulfate pulp having a moisture content of 20% was cut into squares of 40 mm. After being cut, the edges of the squares were brushed with ethylene glycol in the same way as in Example 1, to an absorbed amount of approximately 4%, calculated on the dry weight of pulp in the cutting zone.

A series of sample pieces were dried for 15 hours at 60 C., and another series for the same time at 100 C. Thereafter, the samples were defibrated in water and laboratory sheets were formed from the fiber suspensions obtained. The sheets were then glazed in the laboratory calender. At the same time corresponding sheets were produced, the cut edges of which were not treated. The number of fiber-knots obtained are set out in Table IV.

TABLE IV Number of fiber-knots per dm.'-

Sample 60 C. 100 C.

Untreated 150 150 Treated with ethylene glycol. 30 60 It can be seen from the table that when applying the method according to the invention, a strong reduction in the number of fiber-knots was obtained when the test pieces were subjected to drastic conditions.

EXAMPLES 7 to 14 Glazed laboratory sheets were produced in the same way as in Example 6, but were brushed with 15% aqueous solutions of various salts instead of with ethylene glycol. The salts used and the results obtained are set out in Table V below.

. Potassium chloride As can be seen from the table, a pronounced reduction in the number of fiber-knots was apparent in the sheets treated according to the invention, particularly when sodium acetate, sodium dihydrogen phosphate and calcium chloride were used.

The foregoing examples show the application of the invention under very extreme conditions, starting from the material where the ratio of knot-free pulp to knot-containing pulp is very small. In normal operating conditions this ratio is naturally much greater, which means that the pulp treated according to the invention would be practically free of difiicultly defibred fiber-knots.

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. A method for inhibiting the formation of fiber knots which are diflicult to defiber in cut cellulose paper pulp sheet, which includes the steps of (1) water-laying a wet cellulose paper pulp sheet, (2) removing water from the paper pulp sheet at least to a moisture content of about 20%, and then, in any order, (3) cutting the cellulose paper pulp sheet and (4) incorporating only at the cutting zone of the cellulose paper pulp sheet in an amount of at least 0.1% by weight of the dry pulp, a water-soluble substance capable of (a) swelling the cellulose fibers, or (b) absorbing water from the air, or (c) preventing the contact of fibers by its presence, or (d) lowering the surface tension of pulp-bonded water, to maintain the cellulose fibers of the pulp spaced apart sufiiciently to inhibit formation of cross-links by bonding between adjacent cellulose molecules of the fibers during further drying of the fibers.

2. A method as claimed in claim 1, wherein the watersoluble substance is a substance which causes the fibrous material to swell and which remains in the fibers during drying.

3. A method according to claim 1, wherein the watersoluble substance is a hygroscopic substance.

4. A method according to claim 1, wherein the watersoluble substance is a substance capable of lowering the surface tension of capillary-bound water in the pulp.

5. A method according to claim 1, wherein the watersoluble substance is a substance which prevents the fibers from coming into contact with each other.

6. A method as claimed in claim 1, wherein the substance is added in the form of an aqueous solution.

7. A method as claimed in claim 1, wherein the substance is a polyhydric alcohol having a molecular weight within the range from about 60 to about 1500.

8. A method as claimed in claim 7, wherein the substance is selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, polyoxyand poly-ethylene glycol of molecular weight within the range from about 200 to about 1500, propylene glycol, dipropylene glycol, tripropylene glycol, polyoxyand polypropylene glycol of molecular weight within the range from about 250 to about 1500, butylene glycol, dibutylene glycol, tributylene glycol, polyand polyoxybutylene glycol of molecular weight within the range from about 300 to about 1500, and mixtures thereof.

9. A method as claimed in claim 1, wherein the substance is a water-soluble salt selected from the group consisting of alkali metal and calcium salts and mixtures thereof.

10. A method as claimed in claim 1, wherein the substance is selected from the group consisting of polyoxyalkylene glycol ethers and sulfates of the same, polyoxyalkylene alkyl phenols and thiophenols, alkyl aryl sulfonates, esters of sulfuric acid with aliphatic alcohols of 10 to 18 carbon atoms, and poly-1,2-alkylene oxide wetting agents.

11. A method as claimed in claim 1, stance is a member selected from the of sodium chloride, potassium chloride fate and is added to the pulp.

12. A method according to claim 1, wherein the substance is in an amount within the range from about 0.1 to about 25% based on the dry weight of the pulp.

13. A cut cellulose pulp sheet prepared according to the method defined in claim 1.

14. Cut cellulose pulp sheet as claimed in claim 13 having the substance incorporated in a zone not greater wherein the subgroup consisting and sodium sul- 9 10 than about 10 mm. deep from the outer edges of the FOREIGN PATENTS sheet.

References Cited 586,938 11/1959 Canada.

UNITED STATES PATENTS S. LEON BASHORE, Primary Examiner 2,032,645 3/1936 Youtz 162158 X 5 F- FREI, Assistant Examiner 2,957,797 1 0/1960 Nakayama 162-158 3,316,141 4/1967 Bergholm et a1 162-100 3,414,469 12/1968 Brown et a1. 162100 X 162-12, 76, 77, 82, 87, 164, 181, 194

(333 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 499. 823 Dated March L0, 1970 Inventor) Ingemar Liss-ilbin Croon 51d Lgrs-Gunng r Samuelssgn It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

FColumn 3, line 5, "mixture" should be mixtures Column 3, line 59 and line '74, "Where" should be When Column 6, line '70, "dired" should be dried Column '7, line 47, "drying" should be inserted before "conditions".

SIGNED KND SEALED JUL 2 81970 SEAL) Am M' mm 1:. sum. .112. Meeting Officer Commissioner of Patents 

